1. Field of the Invention
The present invention relates to a street sweeper comprising a frame adapted for travelling over the ground and having at least two transversely spaced wheels, a spring suspension means mounted between each wheel and the frame, a rubbish receptacle mounted on the frame, an elevating conveyor mounted on the frame and having a lower end situated in the region of the two wheels, therebetween, and an upper end situated above the receptacle, and an elongated pick-up rotary broom or rotary brush extending transversally adjacent to the lower end of the elevating conveyor for sweeping the rubbishes on the ground and projecting them into transporting elements (buckets, cleats or vanes) of the elevating conveyor.
2. Description of the Prior Art
The efficiency of collecting rubbish, dirt or refuse by the elevating conveyor depends, to a large part, on the distance between the ground and the transporting elements of the elevating conveyor, when these elements are situated at the lowest point of their travel, and on the constancy of this distance.
From the collecting efficiency point of view, this distance must be as small as possible, but a sufficient clearance from the ground must be maintained so as to avoid any sudden contact between the transporting elements of the elevating conveyor and the ground due to possible irregularities in the street surface or due to the action or depression of the spring suspension means of the wheels (generally the rear wheels) as a consequence of said irregularities.
To overcome this problem, it is known either to use a carrier vehicle not having any rear wheel spring suspension means (or having a suspension with very small flexibility), or to use a carrier vehicle having a rear wheel spring suspension means and an elevating conveyor having an auxiliary frame which is pivotable vertically with respect to the main frame of the carrier vehicle between an upper position for a transport mode and a lower position for a sweeping mode, said auxiliary frame being pivoted to its lower position in response to the actuation of actuating means coupled thereto, and lock out means responsive to the actuation of said actuating means to lock out the spring suspension means when the auxiliary frame of the elevating conveyor is in its lower position for the sweeping mode (U.S. Pat. No. 4,171,551).
The first solution offers the advantage of simplicity, but it does not give the operator a confortable drive during both transport and sweeping modes, and it does not allow standard trucks to be used as carrier vehicles for the rear suspension springs thereof are too flexible. This solution means that a specially designed carrier vehicle must be provided for the street sweeper.
With the second solution (U.S. Pat. No. 4,171,551) a standard truck can be used as carrier vehicle, but it leads to a heavy and costly design to allow and to cause the auxiliary frame of the elevating conveyor to pivot vertically with respect to the main frame of the truck.
It is also known to lock out the suspension springs on some machines or trucks carrying equipments such as, for instance, hydraulic shovels, excavators, cranes, extension ladders, which require very high stability in operation. In these machines the suspension springs are locked out in a position corresponding either to their minimum load or to their maximum load by means which prevent any action of the springs (see for instance German Pat. Nos. 1,530,917 and 1,802,830 and U.S. Pat. No. 2,997,342). However in this case, the purpose of locking out the springs is not to maintain the work equipment at an optimum predetermined distance from the ground but to give to the machine a stable base with respect to the ground.
The object of the present invention is to overcome the above mentioned problem, in the case where a standard truck is used as carrier vehicle, without it being necessary to mount the auxiliary frame of the elevating conveyor for vertical sliding with respect to the main frame of the truck.